US 2978501 A
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Unite States 2,978,501 STABILIZED 'CARBOXYLIC MONOMERS Quandt Adams, Paducah, Ky., assignor to The B. F. Goodrich Company, New York, N.Y., a corporation of New York No Drawing. Filed June 2, 1958, Ser. N 739,437 3 Claims. (Cl. 26052'6) in the uninhibited or pure state. Because of the violent and exothermic nature of this polymerization it has been found necessary in the past to inhibit the spontaneous polymerization especially during the shipping of these acids by the addition of inhibitors such as hydroquinone, hydroquinone monomethyl ether, p-tertiary butyl catechol, copper salts and the like. However, because such well known polymerization inhibitors are effective only in the range of from about 50 to about 500 parts per million based on the monomeric acid it is generally necessary that the inhibitor be separated from the monomer by a distillation, extraction, or adsorption step before the monomer is ready for use in polymerization.
Polymerizations which are carried out with monomeric acid containing any of the above-mentioned Well-known inhibitors generaly have excessively long induction periods, require exceptionally high catalyst levels and the polymeric products are colored.
Accordingly, it is an object of this invention to provide monomeric alpha-beta olefinically unsaturated monocarboxylic acids which are stabilized against spontaneous polymerization even when aged at 50 C. for at least two weeks. It is another object of this invention to provide stabilized monomeric alpha-beta olefinically unsaturated monocarboxylic acids which are clear and colorless even when aged at 50 C. for at least two Weeks. It is still another object to 7 provide stabilized monomeric alpha-beta olefinically unsaturated-monocarboxylic acids which per so are substantially as useful for preparing polymers as the unstabilized monomeric acid. These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following description and examples.
I have discovered a composition of matter comprising a monomeric alpha beta olefinically unsaturated monocarboxylic acid having from 3 to 4 carbon atoms and atentO having a terminal CH group of at least purity to I which has been added a controlled amount of. from about 2 to about 10 parts per million of phenothiazine as the sole stabilizing ingredient said composition being stable against spontaneous polymerization for a period of'at least two weeks at a temperature of 50 C. but being substantially as useful for preparaing polymers as the unstabilized monomeric acid.
The monomeric acids embodied in represented by acrylic and methacrylic acids.
this invention are The polymerization inhibitor embodied in this in vention is phenothiazine which hasthe structural formula lib vention is from about 2 to about 7 parts per million based on the monomeric acid. The combination'of glacial acrylic acid and 3 parts per million of phenothiazine, for example, remains free of polymer and color after aging at '50 C. for two weeks. On the other hand, the combination of glacial acrylic acid and 3 parts per million of phenothiazine is readily polymerized in aconventional polymerization recipe and is indistinguishable from uninhibited glacial acrylic acidin this respect. 7
The quantity of phenothiazine present in a sample of a monomeric acid is determined by adding to a Nessler tube a 50 ml. sample of the'acid' to be tested, 2 ml. of reagent grade concentrated hydrochloric acid and 2' ml. of saturated bromine water. The Nessler tube is then inverted once for mixing and the red color which develops is compared after 15 minutes with a set a standards previously prepared from stabilizer-free acrylic acid to which were added known quantities of phenothiazine and which had beentreated with hydrochloric acid and bromine water in the above-described manner.
The following examples are given to illustrate the.
products of this invention.
Example I A 22 ml. sample of the acid to be tested is placed in a six dram straight walled vial. The vial is then closed with a polyethylene stopper which has been punctured with a pin for thepurpose of eliminating the pressure differential between the interior and exterior of the vial f which develops on heating, thus preventing loss of the I f The stoppered vialis next placed Phenothiazine in Mixture,
Aging Time at 50 C. p.p.m. s
Polymer formed in less than 5 days.
Polymer formed in less than 7 days. 7
No polymer or color in 14 days. 1 o. v
' D0: 7 i V No polymer or colorin 20 days.
I No polymer, slight color in3t) days. i a 'No polymer, colored in 53 days. p
' 2,978,501 liatented Apr. 4 19 61 No polymer or color in 30 days. 1 r i Similar results were obtained when glacial methacrylic acid was substituted for acrylic acid in the above experiment. Example 11 Glacial acrylic acid-phenothiazine mixtures containing variable amounts of phenothiazine were used in the following polymerization recipe:
G. Glacial acrylic acid 50 Dry benzene 450 Caprylyl peroxide 0.25
Color of Induction Polymer Period, minutes Polymerization,
Phenotliiazine in acid, ppm.
When glacial methacrylic acid-phenothiazine mixtures were employed in place of the acrylic acid-phenothiazine mixtures above comparable results were obtained. The acrylic acid-phenothiazine and methacrylic acid-phenotbiazine compositions embodied in this invention show the behavior of the uninhibited monomers when they are interpolymerized with each other and with other vinyl monomers.
The above examples serve to illustrate this invention which is limited in scope only by the appended claims.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A composition of matter comprising a member selected from the group consisting of acrylic acid and methacrylic acid of at least 95% purity to which has been added a controlled amount of from about 2 to about 10 parts per million of phenothiazine as the sole stabilizing ingredient said composition being stable against spontaneous polymerization for a period of at least two weeks at a temperature of C.
2. A composition of matter comprising acrylic acid of at least purity to which has been added a controlled amount of from about 2 to about 7 parts per million of phenothiazine as the sole stabilizing ingredient said composition being stable against spontaneous polymerization for a period of at least two weeks at a temperature of 50 C.
3. A composition of matter comprising methacrylic acid of at least 95 purity to which has been added a controlled amount of from about 2 to about 7 parts per million of phenothiazine as the sole stabilizing ingredient said composition being stable against spontaneous polymerization for a period of at least two weeks at a temperature of 50 C.
References Cited in the file of this patent UNITED STATES PATENTS 2,035,620 Semon Mar. 31, 1936 2,105,284 Groll et a1. Jan. 11, 1938 2,263,013 Scott Nov. 18, 1941 2,576,009 Goertz Nov. 20, 1951 2,576,094 Barthel Nov. 27, 1951 2,609,343 Saunders et a1. Sept. 2, 1952 2,863,851 OBrien Dec. 9, 1958 OTHER REFERENCES Hackhs Chemical Dictionary, 3rd ed. (1944), page 67.
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